1. Field of the Invention
The present invention is generally directed to the field of removing residual materials from a surface and, more particularly, is directed to the field of removing ion implanted or plasma damaged photoresist materials and metal-containing polymeric photoresist materials from the surface of semiconductor devices.
2. Background of the Invention
Name of Ion-Implantation or Plasma Damaged Photoresist
Contemporary photolithography technologies are widely adopted to define various mask patterns for etching or ion-implantation. In this technology, photoresist materials are coated, exposed to light, and developed to form photoresist patterns, and by using photoresist patterns as masks, patterning, etching or ion-implantation processes follow. Thereafter, the remaining residual photoresist material should be removed for subsequent processing.
Unfortunately, the remaining photoresist residue is likely to be of a different chemical structure and property than those of the photoresist material as initially coated. This difference makes it difficult to remove the remaining residual photoresist material.
During N-well, P-well ion implantation, the masking photoresist is damaged forming a hardened surface layer containing carbon-rich, low hydrogen cross-linked polymer. FIGS. 5 and 6 show a hardened surface layer of photoresist residue. It is extremely difficult to remove such a layer using conventional oxygen based ashing processes. Instead, wet treatment using sulfuric acid, or multi-step dry cleaning using ion-collision phenomenon has been widely adopted in the field to remove such layers. The drawback of wet treatment is that it has a tendency to cause substrate silicon recesses. The drawback of multi-step dry cleaning is that it is complicated, expensive and time consuming.
Accordingly, there is a need for a method of removing the remaining residual photoresist material in a simple, low-cost, and efficient manner.
Nature of Via-Etch Induced Polymer
When forming via contact holes connecting lower and upper metal layers in intermetal dielectric(IMD) materials (such as aluminum in via hole), via-etch induced, metal-containing hard polymer materials become coated along the sidewalls of via contact holes by virtue of sputtering during over-etch. Such polymer materials usually contain F (fluorine), which is derived from via etching gas components, as well as metal from metal lines. The chemical composition of such polymer can be generally represented as MCxFyOz, where M is a metal atom, e.g., Al or Ti, and x, y, and z are 0, 1, 2, or 3 and so on.
In an effort to enhance polymer removal ability, it has been suggested to apply fluorine containing gas. However, the use of fluorine containing gas is not a desirable solution from an environmental perspective. Additionally, it is difficult to control and limit or contain the action of fluorine Moreover, fluorine containing gas does not present a completely acceptable or desirable solution from the perspective of incompatible or conflicting process considerations as well as from the consideration of undesirable attacks on underlying oxide materials in a semiconductor device.
Plasma Processing Systems
Plasma has been widely used to deposit or etch various materials on a surface. The use of plasma processing systems is disclosed, for example, in Russian Patent Nos. 2,032,281 (Mar. 27, 1995) and 2,075,135 (Jan. 13, 1995), (PCT International Publication No. WO96/21943) (inventors O. V. Siniaguine and I. M. Tokmulin), and these references are incorporated herein in their entirety by reference. In the system disclosed in Russian Patent No. 2,032,281, two or four electrode units emit jets of plasma carrying gas. The jets carry electric current, and the direction of the jets is controlled by forces generated by interaction of this current with magnetic fields created by the system. FIGS. 1 and 2 show a typical atmospheric plasma jet system employing two torches.
The plasma jet system disclosed in Russian Patent No. 2,075,135 has a plasma jet generator, a gas supply means, and a set of holders for wafers to be treated in a closed chamber. The holders are made in the form of a horizontal platform to rotate about an axis passing through the geometric center thereof perpendicular to the horizontal platform. Each holder is also made to spin about an axis passing through the geometric center of the holder perpendicular to the plane of the holder. FIG. 3, is a schematic diagram that shows this dual rotational arrangement. The plasma jet is directed from the bottom upwards towards the horizontal platform of the wafer holder. Associated with the wafer holder is a manipulator or handler that delivers and retrieves wafers from the holder to a storage device that stores wafers. In operation, a wafer is selected by the manipulator or handler from the storage device and placed in the wafer holder inside a chamber. The manipulator is removed from the chamber, and the chamber is closed. The holder is made to rotate about its axis and thereby expose each wafer in the wafer holder to the action of the plasma jet. In the case of loading a series of holders in the form of a horizontal platform, the entire platform is also made to rotate about its geometric center in order to afford equal and uniform exposure of each wafer to the plasma jet. After treatment, the treated wafers are removed from the wafer holders by the manipulator or handler, and a new batch of wafers are placed in the wafer holders by the manipulator or handler for treatment by the plasma jet.
Plasma generation and plasma processing of materials is also disclosed in U.S. Pat. No. 5,767,627 to Siniaguine which is also incorporated herein in its entirety by reference. This reference discloses a plasma generator having a pair of electrode units for generating a plasma flow in a first direction towards or away from the second plasma flow, and a second magnetic field generator for moving the first and second plasma flows in a direction.
Since polymers having oxidized or fluorinated metal, e.g., Alxe2x80x94O or Alxe2x80x94F, are chemically very stable, these types of polymer materials are very difficult to completely remove using conventional ashing techniques, such as those techniques that are oxygen (O2) based. In the case of conventional oxygen (O2) based, low pressure, radio frequency (RF) plasma ashing, due to the longer mean-free-path of ions, as compared with a plasma jet system, more ions can survive and reach the surface of a wafer, which results in charge-up damage to the devices. Moreover, as previously mentioned, F containing gases like CF4 have to be introduced to completely remove the polymer, and such an introduction is not a desirable solution in view of process compatibility issues and environmental issues as previously mentioned.
As previously mentioned, ion implanted or plasma damaged photoresist residue has a hardened surface coating layer of a different chemical structure and property than those of the photoresist material as initially coated. Referring to FIGS. 5 and 6, the hardened surface coating layer is multi-layered having different chemical compositions. Carbonized or graphitized layers having carbon-rich and low-hydrogen properties and metal-doped, carbonized layers of cross-linked polymer having a 3D-network structure containing impurities and dose-oxide compound residue are formed. The carbonized layer is rigid and brittle. As is well known in the art, this hardened layer is not easily removed using conventional plasma ashing.
Any remaining photoresist residue or incomplete ashing may act as a particle source or affect various electrical characteristics. Accordingly, complete removal of the photoresist residue having a hardened surface layer, which is formed during ion-implantation or plasma etching, is critical to the manufacture of reliable semiconductor device and related or like products.
FIGS. 9 and 10 show the hard polymer just after the via hole etching is completed. Hard polymers containing metal components are formed over the entire wafer surface. From FIGS. 9 and 10, it is apparent that a polymer material having a thickness of a few hundred xc3x85 exists along the via sidewalls.
Referring to FIGS. 11 and 12, a substantial portion of this polymer material along the via hole sidewall is left after conventional photoresist ashing is carried out This kind of polymer material is extremely difficult to remove, because it normally has a very low vapor pressure. The remaining residual polymer material affects contact resistance and thus causes serious reliability problems as related to the functions of the devices. Therefore, complete removal of the hard polymer material, which is formed during the via hole etching step, has crucial importance to the manufacture of reliable semiconductor devices.
While the use of plasma generating systems have been employed to etch materials from surfaces, none of the prior art plasma systems provide completely satisfactory removal of metal-containing polymeric photoresist material from the surface of semiconductor devices. Accordingly, the present invention addresses this need for a more satisfactory method for complete removal of metal-containing polymeric photoresist material from a surface, especially the surfaces of semiconductor devices as well as from the surface of other types of similar materials, including plates, sheets and wafers, substrates, printed circuit boards, compact disks and other products.
According to a feature of an embodiment of the present invention, there is provided a method of removing metal-containing polymeric material and ion implanted photoresist or plasma damaged photoresist from a surface using a plasma jet system, comprising generating radicals having high energy and high density from atmospheric plasma by introducing a reactant gas to the plasma, and placing the surface at a distance from the plasma, whereby ionic reaction on the surface is minimized while the removing action of the radicals on the surface is maintained between about 100 to about 300 degrees centigrade. The flow rate of oxygen may be between about 1 to 5 liters per minute.
In accordance with another feature of an embodiment of the present invention, an atmospheric downstream plasma jet (a form or derivative of arc plasma) system is employed. By utilizing high density and high energy are plasma generated by the equipment, oxygen radicals of relatively high density are generated and used for ashing to completely remove via polymer residues (in other words, metal containing hard polymer) having relatively stable and strong chemical bonding.